The purpose of the proposed study is to investigate the hypothesis that aging in man is accompanied by an increase of sympathetic nervous system activity which has significant physiological effects on the whole organism. The major tool to be used in these studies to assess sympathetic nervous system activation will be plasma levels of catecholamines. One series of studies will investigate whether there is an age-related change of the circadian rhythm of norepinephrine release and whether increased plasma norepinephrine with age is a cause or a result of the alterations of sleep patterns that occur with aging. The second series of studies will investigate whether there is an age related increase of sympathetic nervous system and other neuroendocrine responses to nonbaroreceptor mediated stimuli. Norepinephrine release and tissue norepinephrine stores will be assessed by responses to alpha adrenergic blockade and tyramine, respectively. Release of epinephrine, ACTH, and vasopressin will be tested by responses to hypoglycemia and to a mental stress test. A third series of studies will determine whether there is an age-related change of in vivo catecholamine removal rate and whether metabolic and cardiovascular tissue sensitivity to catecholamines is affected by age. Finally, studies are proposed to investigate whether changes in glucose tolerance and cognitive function which occur with aging are related to increased adrenergic activity.